Archive for September, 2010

Over at Freakonomics, Steven Dubner wonders about the ethics of dimming headlights in the face of oncoming traffic (e.g., why do drivers perform this everyday altruism in the face of seemingly small consequences for not doing so). He also asks: “What I’d like to know is whether the benefit of dimming your headlights — that is, the benefit of not blinding the oncoming driver — is indeed larger than the benefit of keeping your own brights burning?”

This is a question that people who study vision and lighting and driving have thought about a lot. To summarize a conversation I had with Michael Sivak, at UM-TRI, there’s three distances involved here: The legally required distance to dim one’s lights in the face of oncoming vehicles, the optimal distance for maintaining one’s own visibility (and, I suppose, not blinding the other), and then what drivers’ actually do. Readers of this blog will suspect the last factor does not often match up with the two previous factors (and, I should add, as with many things in driving, the scientific issues around night-time illumination are much more complex than the “average expert driver” — i.e., everyone — realizes).

From a pure visibility point of view, opposing drivers should never dim their lights, but should drive on high beam through the whole meeting process. There are, however, certainly other reasons for dimming the lights, such as discomfort glare and fatigue over a longer period with repeated high-beam meetings.

The study of Helmers and Rumar (1975) indicates that the improvements in the low beam since the fifties and sixties have been considerable. That is probably the main reason why the high-beam visibility curve and the low-beam visibility curve in later studies do cross each other—at least when the intensity differences between the two opposing high beams are not too large (about triple or less).

When the two opposing high beams differ substantially in intensity, the visibility differences between the two opposing drivers are quite pronounced (see Figure 3). In such situations, it is most probable that the driver with the weaker high beams will be the one who wants to initiate the dimming, because the driver with the weaker high beam experiences substantial disability and discomfort glare. On a straight, flat road, such a driver will want to dim the high beams at a very large distance between the vehicles.

An early dimming means that both drivers will have to drive on low beams for an extensive part of the meeting process. However, as stated above and illustrated in Figures 2 and 3, at larger separations low beams normally offer shorter visibility distances than high beams. This means that an early dimming leads to short visibility distances for a greater distance traveled, for both opposing drivers.

From a new traffic-themed issue of Philosophical Transactions of the Royal Society, I was particularly interested in an article by Mark Campbell, et al., “Autonomous driving in urban environments: approaches, lessons and challenges.” As I discuss vis a vis Stanford’s “Junior” in Traffic, the perceptual and interaction dynamics of autonomous driving are infinitely complex. Here’s one bit, which follows a case study in which a vehicle had executed a maneuver that, while not being against the safety rules per se, were “still undesirable” — because, in essence, the vehicle, despite being equipped with formal Bayesian estimators and the like, had failed to take into account for what other vehicles might due. In other words, how do you program a vehicle to “expect the unexpected”?

In order for autonomous driving to reach its full potential, it is vitally important that the cars cooperate in the sense that they agree on traffic rules, whose turn it is to drive through an intersection, and so forth. For this, robust agreement protocols must be developed. Recent work on how to make multiple vehicles agree on common state variables, e.g. using consensus or gossip algorithm (Boyd et al. 2006; Olfati-Saber et al. 2007), provides a promising starting point for this undertaking.

When running such agreement algorithms, it is conceivable that not all vehicles will cooperate. They may, for example, be faulty, or simply driven by human operators, and such vehicles must be identified and isolated in order to balance autonomy with human inputs. This will be true on individual cars, but even more so in mixed human–robot networks. Questions of particular importance (that will have to be resolved using the available interconnections) include the following. (i) Safety: autonomous cars must be able to identify human-driven cars and then not drive into them even though they may violate the robot driving protocol. (ii) Opportunism on behalf of the human drivers: people are already driving badly on the road when the other cars are driven by people. How will they act if no-one is driving? This needs to be taken into account by the autonomous cars (i.e. not only will people not follow the ‘correct’ protocol—they might be outright hostile). (iii) Collaborative versus non-collaborative driving: how should non-cooperative vehicles be handled in an algorithmically safe yet equitable manner?

Igor Sikorsky was nothing if not optimistic about the idea of a personal helicopter for everyone (an idea that should now send any reasonable person to the brink of terror) in this 1942 article in The Atlantic.

A question certain to trouble you is this: With hundreds of thousands, perhaps millions, of helicopters flying in all directions at once, what about sky congestion and air traffic problems?

This problem has been foreseen and already a certain amount of planning has been done. While air traffic problems will not be at all comparable to what we now have with the motorcar, there must certainly be one-way air lanes within the limits and in the neighborhood of big centers of population. There will be “slow” and “fast” altitudes and you will choose the one that suits your temperament. Naturally, all helicopter highways will be at a safe distance from the airplane levels.

All helicopters, of course, will remain at a reasonable altitude over thickly populated centers. But there need be no such “flight plan ” as airplanes now must often submit to before undertaking a long journey. Helicopter owners will fly at will, bound only by their common sense and some general traffic rules which are easily obeyed in the vast reaches of the sky.

Nor will the strict physical examination that now might prohibit many thousands from flying an airplane be necessary. A person who can drive an automobile can fly a helicopter; and a man or woman with middle-aged reflexes is just as safe in one as in the other because the helicopter, as a rule, is always moving slowly when close to the ground. The helicopter owner will have to pass no stricter examination than is—or should be—necessary for driving a motorcar. He should not be color-blind, his vision should be normal with or without glasses. A man or woman with a heart ailment should not drive a helicopter—nor an automobile.

Bill Beaty, the amateur “traffic waves” scientist described in Traffic, writes in to describe his early experiences with Seattle’s new Active Traffic Management System — the “dynamic” system of varying speeds, imported from Europe, which is meant to ameliorate the impact of drivers driving into vast stop-and-go traffic (with the ensuing shockwaves).

Beaty was curious to note that the first part of the project is happening on the very section of I-5 where he first began developing his one-man crusade for traffic harmonization. Here’s how he describes his new commute, which seems to have some of the disequilibrium that new schemes bring:

In the first week it created very strange patterns: huge I-5 jams on
Sunday (when Sunday I-5 northbound has always been empty.) They now seem
to be tweaking their algorithm. Or perhaps drivers are no longer freaking
out. Patterns are still odd, but keep changing over many days.

From what I can see, they’re trying to limit the inflow to the daily
northbound jam at I-5 and I-90 interchange. The result is a large
slowdown far south of the city, with an empty region right at the location
of the daily jam. Very odd to encounter a major slowdown near my own home,
where there never was congestion before …but then at the usual location
of the giant I-5 snarl, the traffic flows free at 50mph. Presumably there
no longer exists any continuously-growing daily jam. Merging at city
exits has suddenly become easy. Probably the old jam has been converted
into shockwaves moving slowly backwards, rather than the previously huge
region of 20mph driving.

Another ATMS section is on I-520 …which is right where I first saw the
string of headlights that inspired my first online article. Bizarre
coincidences. Or maybe the bigwigs in the Seattle traffic control
community have all been reading my site?

Any other Seattle-area readers/engineers care to share their experience?

And speaking of commute times, Harry Kao writes in to tell me he has created a Google Maps visualization based on the bit in my book about the historical constancy (in some cases) of commute times. You can find it here (click on the map to engage).

And here are the details, which Kao notes need refining (and I wonder how this differs from WalkScore’s new “Commute” tab). Perhaps someone out there can help?

The primary data source is the CTPP 2000. This survey was sent to a subset of households during the 2000 Census and records, among other things, where people live and work.

The CTPP has since been superseded by the ACS. Although transit statistics from the ACS have been published more recently, the the new data is not sufficiently fine-grained for use with this map.

The CTPP provides data on a census tract level. However, this map uses zip codes to identify regions because they’re more familiar to most people. The mapping from census tract to zip code is done by using the Census Zip Code Tabulation Areas (ZCTAs) to determine the proportion of each census tract that falls within each zip code and weighting the CTPP data accordingly.

The Google Maps API is used to determine routes and transit times. The usual caveats apply. In particular, it is assumed that all commuters drive during non-peak hours. This is surely incorrect (but it’s the best that I can do) so the trip times are likely to be underestimates.

People looking into the effects of long commutes have found everything from higher stress levels to fewer social relationships, but a new study by Jos N. van Ommerenlow and Eva Gutiérrez-i-Puigarnaua, published in Regional Science and Urban Economics, throws another factor into the mix: The tendency for employees to show up for work.

Our results indicate that, ceteris paribus, commuting distance has a strong positive effect on absenteeism, with an elasticity of about 0.07 to 0.09. In the hypothetical case that all workers in the economy have a negligible commute, absenteeism would be about 15 to 20% lower, roughly one day per year, so the results are economically relevant. Our favoured interpretation is that the effect identified is predominantly through an effect of the time component of commuting costs on voluntary absenteeism in line with Ross and Zenou, 2008 (S.L. Ross and Y. Zenou, “Are shirking and leisure substitutable? An empirical test of efficiency wages based on urban economics theory,” Regional Science and Urban Economics 38 (5) (2008)), but we cannot completely exclude the possibility that some of the effect is through an effect on health and therefore on involuntary absenteeism, as argued by Zenou (2002).

Reading the various stories recently about driving on beaches, as vexing for safety reasons as environmental and simple quality of life factors, I couldn’t help but think back to Edward Abbey’s classic reproach, in Desert Solitaire, to those tourists who traveled via car in the national park at which he was stationed. I know Abbey the man is something of a thorny subject but the book is one of those rare titles that leaves an incendiary impression, the date and place of first reading forever fixed in one’s mind.

What can I tell them? Sealed in their metallic shells like mollusks on wheels, how can I pry the people free? The auto as tin can, the park ranger as opener. Look here, I want to say, for godsake folks get out of them there machines, take off those fucking sunglasses and unpeel both eyeballs, look around; throw away those goddamned idiotic cameras! For chrissake folks what is this life if full of care we have no time to stand and stare? Take off your shoes for a while, unzip your fly, piss hearty, dig your toes in the hot sand, feel that raw and rugged earth, split a couple of big toenails, draw blood! Why not? Jesus Christ, lady, roll that window down! You can’t see the desert if you can’t smell it! Dusty! Of course it’s dusty – this is Utah! But it’s good dust, good red Utahn dust, rich in iron, rich in irony. Turn that motor off. Get out of that piece of iron and stretch your varicose veins, take off your brassiere and get some hot sun on your old wrinkled dugs! You sir, squinting at the map with your radiator boiling over and your fuel pump vapor-locked, crawl out of that shiny hunk of GM junk and take a walk – yes, leave the old lady and those squawling brats behind for a while, turn your back on them and take a long quiet walk straight into the canyons, get lost for a while, come back when you damn well feel like it, it’ll do you and her and them a world of good. Give the kids a break too, let them out of the car, let them go scrambling over the rocks hunting for rattlesnakes and scorpions and anthills – yes sir, let them out, turn them loose; how dare you imprison little children in your goddamned upholstered horseless hearse? Yes sir, yes madam, I entreat you, get out of those motorized wheelchairs, get off your foam rubber backsides, stand up straight like men! like women! like human beings! and walk – walk – WALK upon our sweet and blessed land!

A colleague sends the above photo of a “double roundabout,” in Buffalo, NY (or it’s suburbs). While your first thought might be, wow, how confusing, consider the Google Map image below that shows the original intersection — too big, actually two intersections masquerading as one (one can imagine cars getting “trapped” in that little extra segment, and box-blocking problems). Undoubtedly there was a crash problem, hence the double roundabout. Which are used in the U.K. (and taken to its logical extension in the “Magic Roundabout”, of course, but are, as far as I know, relatively novel here. Anyone live near here by chance and care to weigh in?

An interesting prototype design via the PFSK Conference for an “ergonomic” crosswalk that takes into account pedestrians’ natural inclinations to want to shorten the distance it takes them to cross the street (as someone once told me, ‘pedestrians are natural Pythagoreans’). I can foresee a problem with cars, who already stray into the crosswalk, having a bit of a problem lining up. And while I like the red/yellow LED light concept in theory, does it just lessen our tendency to look at the actual environment for safety cues?

Motorists travelling on 22nd Street in West Vancouver will be confronted with a 3D image of a little girl chasing a ball in the street starting next Tuesday. The girl will be an optical illusion, but the scenario is very real, according to David Dunne of the BCAA Traffic Safety Foundation.

I’m all for illusion-based traffic calming techniques that create the sensation that drivers are driving faster than they really are — and I realize there is no greater challenge in traffic engineering than managing driver speed — but I would have reservations about putting an imaginary obstacle in the middle of the road (perhaps putting the child on the side of the road would be merely enough?). For one, it may, however unlikely, provoke the driver into taking evasive action, thus getting into real trouble. For another, the presence of false hazards may reduce our vigilance to real hazards. And one wonders if this would open the door to 3-D billboards and other projections.

What better way to conclude the Australasian Road Safety Conference, thought me, then to head out for a spot of cycling in Canberra, where spring is just on the wing. My guide was Ashley Carruthers, an anthropologist and member of local advocacy group Pedal Power (and my ride was a surprisingly nimble fold-up Dahon). Canberra is one of those intensely planned capital cities, its geography dictated by fiat and compromise, its layout and design (via the American Walter Burley Griffin) evoking, to my mind, D.C. — though, as Carruthers noted, reputedly infused with esoteric and hieroglyphic meanings. While the city, cycling wise, hasn’t gotten the attention of, say, Melbourne, with its new sharing scheme, Pedal Power boasts a large and active membership, and there’s a fairly wide trail network (though not much evidence of on-street cycling, in the area I was staying, at least).

Now, about that magpie, which I had tweeted about briefly in reference to its intoxicating song. It turns out they can be rather fierce enemies of those on bikes, swooping down from trees to land on their helmets and peck at their ears. As a countermeasure, riders will strap plastic twist-tie-like things to their helmets, virtually sprouting of their heads like gangly antennae. It was a bit unnerving to find a couple of these fellows coming toward me, the shock troops of some alien two-wheeled race. I’m not sure if this sort of thing happens elsewhere, but it was the first I had seen in such active preparation for avian attack. Yesterday, at least, the magpies were quiet.

How We Drive is the companion blog to Tom Vanderbilt’s New York Times bestselling book, Traffic: Why We Drive the Way We Do (and What It Says About Us), published by Alfred A. Knopf in the U.S. and Canada, Penguin in the U.K, and in languages other than English by a number of other fine publishers worldwide.